Low viscosity and high attenuation in MgSiO3 post-perovskite inferred from atomic-scale calculations
AM Goryaeva and P Carrez and P Cordier, SCIENTIFIC REPORTS, 6, 34771 (2016).
This work represents a numerical study of the thermal activation for dislocation glide of the 100 (010) slip system in MgSiO3 post- perovskite (Mg-ppv) at 120 GPa. We propose an approach based on a one- dimensional line tension model in conjunction with atomic-scale calculations. In this model, the key parameters, namely, the line tension and the Peierls barrier, are obtained from density functional theory calculations. We find a Peierls stress sigma(p) = 2.1 GPa and a line tension T = 9.2 eV/angstrom, which lead to a kink-pair enthalpy (under zero stress) of 2.69 eV. These values confirm that this slip system bears a very low lattice friction because it vanishes for temperatures above approximately 500 K under mantle conditions. In the Earth's mantle, high-pressure Mg-ppv silicate is thus expected to become as ductile as ferropericlase. These results confirm the hypothesis of a weak layer in the D '' layer where Mg-ppv is present. Easy glide along 100(010) suggests strong preferred orientations with (010) planes aligned. Highly mobile 100 dislocations are also likely to respond to stresses related to seismic waves, leading to energy dissipation and strong attenuation.
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